Field and greenhouse experiments were conducted to encourage growth of basal branches of tomato (Lycopersicon esculentum Mill.) through apex removal and use of plastic mulch. In the greenhouse experiment, apex removal (topping) delayed anthesis of the first flowers by 6 days, but then the faster branch growth increased flower cluster numbers more rapidly on topped plants than on untopped plants. In the first field experiment, apex removal and clear plastic mulch stimulated basal branching and led to a 25% increase in yields of the first four harvests, with the combination of treatments having additive effects. Mulching increased leaf concentrations of P, K, Ca, and NO3-N and decreased Na concentrations, whereas topping increased Ca, Mg, and Na concentrations in leaves sampled 24 days after transplanting. In 1985, mulching resulted in a 54% increase in early yields, but topping depressed marketable early yields by 20% because of fasciation (“catfacing”). In 1985, early yield of an early processing line was stimulated more by mulch than were two later-flowering fresh-market cultivars.
Two experiments were conducted on a gravelly loam soil of low N status to determine the amounts and timing of N fertilizer needed for high early and total yields of fresh-market tomatoes grown with or without clear plastic mulch. In both years, the mulch slightly increased early flower number, hastened flower production, and increased early yield. Hastening of maturity of plants on mulch resulted in a 22% increase in ripe fruit in the short (118-day) season of 1984 and a decrease in percent green fruit at final harvest. A N rate of 84 kg·ha−1 increased total yields compared to 0 N, whereas 168 kg·ha−1 of N decreased early yield in 1984 but not 1985. Applying one-half of the N at planting and sidedressing the remaining half was just as effective in increasing yields as applying all the N at planting, even with mulched plants. Low tissue NO3-N concentration (< 0.2%) 3 weeks after transplanting reflected insufficient N application for optimum yield but also resulted from limited soil moisture when applied N was adequate. The mulch has increased P consistently and, to a lesser extent, the K concentration in young tomato plants, whereas the effects of mulch on mineral concentration of other elements have varied with year, soil type, and climatic factors.
Two field experiments were conducted with two cultivars of transplanted tomatoes (Lycopersicon esculentum Mill.) with and without plastic mulch, varying the initial rate of N fertilizer, but maintaining the total N rate at 168 kg·ha–1 by sidedressing. In 1982, 0 and 112 kg·ha–1 initial N rates, and bare ground, black mulch, and clear plastic mulch were compared on a gravelly loam soil. In 1983, initial N rates used were 34, 67, 101, or 134 kg·ha–1, with bare ground and clear mulch on a silt loam soil. Effects of the plastic mulch dominated both experiments. Mulching increased rate of basal branch appearance and led to early flowering on branches. Total plant growth, as measured by vine weights at final harvest, was increased by mulch in both years. Mulching increased early yield only in 1983, but increased total yields by 13% and 79% in 1982 and 1983, respectively. Initial N fertilizer rates did not influence total yields significantly in either experiment, although high initial N rate, combined with clear plastic mulch, led to a significant decrease in percent marketable fruit in 1982. In 1983, mulching increased shoot concentrations of N, NO3-N, P, K, Ca, Mg, Cu, and Β (P = < 0.01) in spite of the fact that mulched plants were larger than unmulched plants at sampling time, 24 days after transplanting. Nitrogen fertilizer increased only the N and P concentrations and to a lesser extent than did the mulch.
Growing a main vegetable crop for harvest and a cover crop for residue return to soil in the same growing season is a promising strategy to sustain soil quality in vegetable rotations. Our research evaluated cover crop strips interseeded between pumpkins (Cucurbita pepo L.) as a way to implement such a strategy. Cover crop types were lana vetch (Vicia villosa ssp. dasycarpa Ten.) and a lana vetch–winter rye (Secale cereale L.) mix, interseeded before, at the same time, or after pumpkins. The competitive impact of different cover crop strips was assessed using pumpkin yield, cover strip biomass, crop nitrogen status, soil nitrate status, and soil water potential. Cover strips were also assessed for competitiveness with native weeds. Seeding date affected the competitiveness of cover strips with pumpkins, while cover type did not. Cover crops seeded before pumpkins or at the same time reduced pumpkin yield in proportion to biomass produced by the cover strips early in pumpkin growth. Cover strips seeded after pumpkins did not reduce yield. Tilling in a before-seeded cover strip at 30 days after pumpkin seeding gave higher pumpkin yield than before-seeded cover strips that were not tilled. At three of four sites, after-seeded cover strips had the lowest percent weed biomass in strips, and at two sites with moderate weed pressure vetch–rye strips were more effective than vetch alone in suppressing weeds. Cover strips seeded before or at the same time as pumpkins reduced pumpkin yield by taking up resources that were otherwise available to pumpkins. At a high-rainfall site, competition for soil nitrate by cover crop strips was the dominant factor in reducing pumpkin yield. At a low-rainfall site, the dominant factor was competition for water. Because of effective weed suppression and lack of pumpkin yield reduction, interseeding vetch–rye strips after pumpkins was a promising practice, as was tilling in preexistent cover strips at an interval <30 days after pumpkin seeding. Good previous weed management and rye–vetch mixes at high seeding rates are necessary to allow interseeded cover strips to outcompete weeds.
Under conditions of environmental stress, many pepper (Capsicum annuum L.) cultivars lose flower buds, probably due to production of the abscission-causing hormone ethylene. Field applications of the ethylene-generating chemical ethephon (0 to 300 µl liter-1) were made to five cultivars of bell pepper growing under nonstressed conditions, but differing in resistance to stress-induced bud abscission. Cultivars were seeded at several times in 1985 to synchronize stages of plant development and allow a single simultaneous spray application to all plots. In the two 1986 experiments, all cultivars were sown on the same date and either two or three sprays were applied to all plots to more closely approximate screening conditions used by plant breeders. One week after application of ethephon at 300 µl.liter-1, virtually no flower buds remained on any cultivar in either year. Susceptible cultivars exhibited significantly greater abscission than resistant ones at ethephon concentrations of 75 to 200 µl.liter-1. The use of ethephon shows promise as a simple screening method for resistance to stress-induced flower bud abscission in pepper. Chemical name used: 2-chloroethyl phosphonic acid (ethephon).
Dry beans (Phaseolus vulgaris cvs. Red Kidney and Great Northern) were grown in the cool season in the lowland tropics at Los Banos, Philippines. Manual removal of flowers for 11 days from first bloom resulted in increased wt of vegetative parts and no change in rate of total dry wt gain. New branches, roots, and leaves provided efficient alternate sinks for assimilates, so that leaf area was increased and maintained longer, and more branches formed. Although temporary flower removal increased pod set compared to control plants, pod and seed abortion prevented a significant yield increase. This resulted in lower ratios of seed wt to total dry wt, and decreased pod wt production per unit leaf area.
A series of field and greenhouse experiments was conducted with three cultivars of bell pepper (Capsicum annuum L.) to determine the hormonal basis for flower bud and flower abscission as induced by low light intensity (LLI). Imposition of 80% shade for 6 days increased abscission of reproductive structures by 38% and resulted in an increase in bud ethylene production. Concomitantly, bud reducing sugars and sucrose decreased and these were negatively correlated with ethylene levels and those of its precursor, ACC. Infusion of ACC into the pedicel resulted in flower bud abscission within 48 hr. The results indicate that ethylene is the primary causal agent of pepper flower bud abscission. Production of auxin by the bud plays a role in prevention of abscission. The abscission of disbudded pedicels was prevented by infusion of NAA. Although the three cultivars had similar responses to ACC, they differed in the amount of abscission under stress, bud sugar levels, and the time of onset of ACC and ethylene production. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); α-napthaleneacetic acid (NAA); (2-chloro-ethyl)phosphonic acid (ethephon).
Tomato (Lycopersicon esculentum Mill.) plants grown on polyethylene (PE) mulch in New York State frequently have more branches and increased mineral nutrient uptake and yield than plants not mulched. In four field experiments conducted on a silt loam soil, clear PE mulch stimulated root extension shortly after transplanting. One week after transplanting, roots were significantly longer for mulched than for unmulched plants in all four experiments, whereas aboveground dry matter differences did not become significant until 14 days after transplanting in two of four trials. Mulching increased branching, hastened flowering on basal branches, and increased concentration of major nutrients in the aboveground parts. In the field, stimulation of aboveground growth due to mulch might be brought about by warming of the stem by air escaping from the planting hole in the mulch. However, an experiment with black, white, or clear mulch, in which the planting hole was either left uncovered or covered with soil, showed no effect of hole closure on branching even though air temperature near the stem was increased when holes were left uncovered. The results taken together imply that the increased aboveground growth observed with mulching is a consequence of enhanced root growth and nutrient uptake.
Although it has been known since the 1930s that long photoperiods and high temperatures hasten bulb formation in onions, the time at which onion cultivars under field conditions in New York start forming bulbs has not been previously reported. In the 1997 and 1998, onion cultivars were seeded in three commercial onion production areas at normal early spring planting dates. In 1998, a time-of-planting study was carried out in Ithaca, N.Y., in which three transplanted crops and three direct-seeded crops were established at monthly intervals beginning at the end of March. Bulb ratios (bulb diameter: neck diameter) were measured at 2-week intervals during the season in all plantings. Initiation of bulbs (assumed to occur 3 weeks before bulb ratio reached 2) was then related to the photoperiod and air temperature up to that point. A comparison of early, mid-season, and late cultivars indicated that bulbs are initiated in commercial plantings in New York at close to the longest day of the year (15.6 h), at a time when mean temperature is still rising. In the time of planting study, delay of planting resulted in fewer days from emergence to bulb initiation and a reduction in growing degree-day accumulation. If planted later than 15 June, some cultivars failed to initiate bulbs, but others, such as `Quantum' and `Winner', initiated bulbs but did not mature them. The results indicate that photoperiod appears to be the primary factor for the initiation of bulbs, but that bulb initiation can be modified strongly in some cultivars by temperature.
High temperatures during flowering frequently limit yields of some bell pepper cultivars in New York fields. Previous research has shown that subjecting the plants to low light at flowering can have similar effects. To determine if cultivar differences in flower abscission and yield could be accentuated by such a shade stress, field plots of six cultivars were subjected to 1 week of low light during flowering. Shade cloth tunnels were erected over the plant rows in two experiments, reducing incident light by 80%. Nondestructive abscission counts were taken at the start, and 7 days after the end of a 7-day shade period. Mature green fruit were harvested periodically. Low light stress resulted in 68% and 86% abscission at the first three fruiting nodes in 1992 and 1994, respectively. Cultivars showed differential abscission in unshaded plots, and after shade, producing a significant cultivar: shade interaction. `Ace' showed least abscission and maintained yields with shading; `Camelot' lost nearly all flowers and buds with low light stress, and was reduced by 75% and 91% in marketable yield in 1992 and 1994, respectively. Results indicate that shade stress accentuates abscission susceptibility in bell pepper cultivars. Pepper lines selected for low light tolerance may show promise in resisting flower abscission at high temperature.